Method of depositing metals and metallic compounds throughout the pores of a porous body



3,160,517 MPOUNDS W. C. JENKIN Dec. 8, 1964 METHOD OF DEPOSITING METALS AND METALLIC CO THROUGHOUT THE PORES OF A POROUS BODY Filed Nov. 13. 1961- INVENTOR WILL/AM G. (JENKIN ATTORNEXfi United States Patent 3,160,517 METHSD 0F DEPflfiTlN G METALS AND METAL- Lllij CQMPSUNDd THRGUGHfiUT THE PGRES 0F A PQROUS BQBY William C. Jenlrin, Dayton, Qhio, assignor to Union Carbide Corporation, New York, NY.

Filed Nov. 13, 1961, Ser. No. 151,779

1 Claim. (tCl. ll7--93.3)

This invention relates to a process of gas plating metals and utilizing thermal decomposition of volatile metal compounds, under critical conditions, to deposit metal or a compound thereof throughout the pores of a porous body.

The known procedures for depositing metals or metallic compounds on porous bodies by thermal decomposition of vaporizable metal compounds results in the deposition of a coating on the surface only. Some small degree of penetration of the gaseous metal compound randomly of the sub-surface may occur. Where gas-vapor mixtures are forced through the porous body, metal deposition occurs on the surface and sub-surface and which blocks or seals this area so that further penetration to the center of the porous body cannot take place. Still other methods tried produce only a very light metal deposit where some penetration of plating gases is obtained. 1

Utilizing the prior gas plating methods it has not been possible heretofore to accomplish an even and uniform deposition of metal or metallic compounds throughout a porous structure such as is now achieved by' the process of the present invention. a

While the invention is described with more particularity to gas plating of metals, the process is broadly applicable to the deposition of metallic compounds, for example oxides, carbides, etc. of metals. The term metallized as set out in the claims hereinafter is thus intended to include both metal and metallic compounds.

In accordance with this invention it has been discovered after considerable experimentation that the deposition of metal and metallic compounds uniformly throughout porous bodies results from observing the following critical conditions- 1) The first requisite condition is the use of lower temperatures than would normally be required to deposit a surface coating by thermal deposition from a vaporizable metal compound;

(2) The second conditional requirement is to heat the porous body in such a manner as to create a temperature gradient within the body, and while thus heated force the gaseous plating mixture through the body from the low temperature side;

(3) The third condition requires the inclusion in the plating gas mixture of a low percentage of at least one of the products of decomposition of the metal bearing compound chosen. The inclusion of such decomposition products suppresses the initially rapid thermal decomposition that normally takes place in the absence of said component, and thereby avoids sealing the pores on the inlet side of the porous body which stops further penetration of the plating gas.

The unexpected results obtained employing these usually low temperature and requisite conditions scribed, are believed to be accounted for because tle plating gas mixture passing through the pores of the heated body and in intimate contact therewith brings about a very rapid transfer of heat to the plat ng gas. Thus the plating gas is quickly heated to the same temperature as the porous substrate. On the other hand,

undewhen depositing metals or their compounds from gaseous metal bearing compounds by thermal decomposition of the same on a fiat or planar surface, heat transfer is 3,160,517. Patented Dec. 8, 1964 relatively slow, so that the surface must be overheated to compensate for this. The use of a low temperature for gas plating porous bodies has been found by test runs to be a criticality which must be observed to obtain successful results and such as achieved by the present invention.

The requirement for the temperature gradient is best explained by the graph below. This isa graph which shows the temperature gradient when employing nickel carbonyl as a thermally decomposable metal compound. It shows the relation between (1) the composition of a plating gas mixture of the metal compound (nickel carbonyl) and a product of its decomposition (carbon monoxide), and (2) the temperature (of the porous substrate) required to maintain an identical rate of deposition for ll plating gas composition. On this graph, rate of deposition is held constant while temperature and composition change.

5 to" a zoo;

tion of the nickel carbonyl as the compound is decomposed; then the plating gas moves to the center of the porous body where the higher temperature (approximately 290 F.) is maintained and the same rate of deposition occurs as from the more concentrated mixture; and

finally the lean mixture'moves on the far side of the porous body where a still higher temperature (310. F.) is maintained and the same rate of deposition takes place.

The sharp drop at the right hand end of the curve illustrates the third required step. A sharp drop in the temperature gradient is required to maintain the same constant rate of deposition Where a plating gas containing nickel carbonyl is employed. Such a sharp gradient is unobtainable and therefore at 100% nickel carbonyl concentration, plating is too rapid at the first surface contacted, and the surface pores .thus become sealed over.

By adding 3% or more, and preferably upto 20 or 25% maximum, of carbon monoxide to the plating gas,-

it has been found that this rapid deposition is avoided along with the disadvantages. Thus by employing a plating gas, as described, and which does not require such a sharp temperature gradient, these difi'iculties are overcome. Other thermally decomposable metal compounds may be used, and wherein a small percentage of one of the products of decomposition must similarly be added to the plating gas.

Unreacted gases of moderate thermal conductivity also may be added, such as carbon dioxide or nitrogen. They do not, however, alter the relationship described, but in some instances shift the temperatures that'are required for good results downward a few degrees.

The best method of obtaining the temperature gradient required has been found by experimental tests to comprise the application of infra-red heat to one side of the porous body while the opposite side is heated only by :onduction and is therefore cooler. A relatively thick porous body generally requires the addition of another and .ower intensity infra-red heat source on the cool side, particularly if the temperature drop is too great. The porous body to be gas plated is preferably mounted in a :entrally located wall in a chamber with an infra-red :ransparent window at one or both ends. The mounting in the wall is vapor tight, so that the plating gas mixture when admitted on one side is forced entirely through the porous body to the other side. 7

A modification of the method described comprises the 186 of low temperatures as aforementioned, but instead bound with a rubber gasket in a central wall of a tubular chamber, such as illustrated in the drawings, at least one end of which has arranged an infra-red transparent window as illustrated in FIGURE 1. Infra-red lamp means or infra-red radiator source directs heat waves against the grinding wheel. The hot grinding wheel surface on the'exhaust side (see FIG. 1) was maintained at 310 F. and the temperature gradient decreased to 290 F. at the inlet side surface of the porous grinding wheel. A plating gas mixture consisting of 100 ml./min. of carbon monoxide, 2 liters/min. of carbon dioxide and 370 ml./

, min. of nickel carbonyl vapors was employed. The car- )f forcing the plating gas mixture through the porous Jody, the body is suspended in a chamber having infra- Ied transparent windows and exposing the porous body :0 infra-red heat while the chamber is continuously supplied with a plating gas mixture consisting of a relatively iigh conductivity gas and vapors of a thermally decomposable metal compound. Under these conditions, the netal constituent of the compound is deposited throughut the porous body.

While it is not known definitely what the chemical or physical reaction is, it is believed that the use of high :onductivity gases, such as hydrogen and helium assist :he vaporized metal compounds and the applied heat in reaching to the interior of porous masses whereby thernal decomposition of the metal compound takes place in :he interior and deposition of metal is plated onto the walls of the porous body structure.

The accompanying drawings illustrate suitable appara- .us for carrying out the gas plating of porous substrate iodies in accordance with this invention.

FIGURE 1 illustrates an apparatus for gas plating a orous grinding wheel employing an infra-red radiator and 'efl'ector, the apparatus parts being shown in section; and

FIGURE 2 is a similar view as in FIGURE 1, and ilustrating the use of a plurality of infra-red radiators and 'eflectors.

In the drawings, in FIGURE 1 a porous grinding Wheel 0 be gas plated to deposit metal evenly throughout the mores is designated 10 and is shown suspended in a gas )lating chamber generally designated 11. An infraed lamp source 12 and reflector 13 are arranged at one Me of the gas plating chamber 11. A window 14 in he side wall of the gas plating chamber 11 permits the nfra-red rays to penetrate through the window and iocus on the grinding wheel 10.

In FIGURE 2 a similarly suspended porous grinding vheel 18 is arranged in a gas plating chamber 20 and re- :eives infra-red ray treatment from the lamps 21 and 52 which suitably are equipped with reflectors 23 and 24 'espectively. The gas plating chamber in this instance :omprises two side wall windows 25 and 26 which are ransparent to the passage of infra-red light rays.

The following examples are exemplary of the invenion but not restrictive thereto.

Example 1 The present invention was utilized for the deposition of netal throughout the pores of a grinding wheel made of )arborundum and having an average porosity. The wheel vas approximately six inches'in diameter and one-half nch thick, and weighing 480 grams. Nickel metal was leposited throughout its porous structure. Such a wheel s abrasive and will conduct electricity. The resultant gas plated wheel may be employed to grind metal subtrates with a high amperage current passing between it tl'ld the work, and results in the removal of stock at an :xtremely high rate.

To support the grinding wheel during gas plating, the :ame is cemented with plaster, or the like, or otherwise tonate in a carrier gas of carbon dioxide.

bon dioxide adds large gas volume movement and insures better distribution of the plating gas in the pores of the grinding wheel. After 4 hours of gas plating approximately 150 g. of nickel metal was deposited. The metal deposit was very uniform from side to side and edge to edge throughout the grinding wheel.

Example 2 Employing a modified method, the same size of grinding wheel had a deposit of approximately g. of nickel applied throughout its porous body in 8 hours. The plating gas in this instance was composed of 200 ml./min. of nickel carbonyl vapor and 200 mL/min. of hydrogen, the mixture being supplied to the'gas plating chamber. The 6" diam. wheel was hung in a 10" diam. chamber with infra-red transparentwindows arranged 4" apart, the grinding wheel was located centrally between the windows, with the plating vapors free to pass all around. An apparatus, such as illustrated in FIG. 2, without the center wall, was employed in this instance. Employing two infra-red radiators as shown in FIG. 2, the rays of the radiator on both sides are focused along a central plane to the porous wheel, no externally generated temperature gradient being required to maintain a temperature gradient throughout the porous wheel as indicated on the graph for gas plating using nickel carbonyl.

Electrical conductivity measurements on such gas plated metal permeated wheels has upon testing yielded values of .01 ohm per square inch and less, and thus indicating that the deposit of metal is continuous and uniform throughout the grinding wheel.

Example 3 In this example the gas plating impregnation of a carbon body by copper metal was effected. Ordinary gra phitic carbon has approximately 20% of voids. A disc of such a porous carbon body was mounted as illustrated in FIG. 1. A suitable heat-decomposable metal bearing compound as used in this example was copper acetylace- Using this copper compound the chamber is surrounded with a heated jacket to avoid condensation of the plating-gas on the Walls of the gas plating chamber. The metal compound is vaporized in a current of carbon dioxide using an auxiliary apparatus and fed to the chamber on the side opposite that where the infra-red heat is directed. A

- small amount of acetylacetone is included in the plating gas mixture to suppress rapid deposition at the surface of the porous graphite body initially contacted by the plating gas. Employing a temperature on the cool side of 400 F. and ascending to 500 F. on the hot side, copper metal is deposited substantially to uniform thickness throughout the graphite body.

Example 4 I mounted and sealed in a center wall of a gas plating chamber such as illustrated in the drawings, with infrared heat applied to one side through a transparent window and a plating gas mixture being forced through theporous body from the opposite side. The plating gas mixture used consists of chromium hexacarbonyl volatilized in an auxiliary chamber, and introduced into the plating chamher with carbon monoxide. An unreactive gas, such as argon is added up to 50% as a carrier gas to facilitate movement and distribution of plating vapors. The temperature of the side oppose the heat is maintained lower than for normal plating, e.-g., 400 F. Because of a temperature gradient varying from 400 F. on the cool side to 500 F. on the hot side and the carbon monoxide addition at this low temperature, the porous body becomes heavily permeated throughout with a deposit of chormium carbide.

Example 5 In this example a high temperature refractory nozzle of tungsten was gas plated and impregnated with ruthenium. Ruthenium is highly resistant to oxidation and its high melting point protects the easily oxidizable tungsten, the latter possessing high temperature strength.

In carrying out the gas plating process, a compressed, sintered tungsten body having 80% of theoretical density was positioned in the plating chamber being sealed in the center Wall of the chamber. Infra-red heat was then applied to one side and a plating gas mixture forced through from the other side. Ruthenium pentacarbonyl as vaporized in an auxiliary apparatus was mixed with 10% by volume of carbon monoxide (CO) and fed to the gas plating chamber. An unreactive carrier gas, argon, was added to achieve better movement and distribution of gas plating vapors. A temperature of about 325 F. was maintained on the hot side, with a temperature gradient throughout the body dropping to 285 F. at the cold side. Gas plating of ruthenium into the pores of the tungsten body is thus accomplished since the metal does not seal the first surface contacted, but deposits heavily throughout the porous body.

Example 6 In this example a graphite disc approximately one-half inch in thickness was gas plated to deposit copper oxide uniformly throughout the porous graphite mass. The gas plating was carried out as described in Example 3 employing copper acetylacetonate in carbon dioxide but employing a lower than normal temperature, and a gradient, such that the cold side is 375 F. and the hot side at 450 F. with the introduction of approximately 1% by volume of oxygen in the plating gas. At this lower temperature and conditions copper oxide deposits substantially uniformly throughout the body of the graphite.

An essential criterion in carrying out the process in order to produce the uniform deposition of metals or their metallic compounds consists of the creation of a temperature gradient within the body of the porous material being subjected to gas plating. This temperature gradient is maintained from a relatively loW temperature adjacent the inlet surface side to a higher temperature on the exit or discharge side of the porous body being treated.

I E) This gradient temperature, of course varies With the gas plating mixture and substrate material being plated.

Generally the temperature gradient will be'within therange from about 250 F. to 500 F. with a temperature gradient curve comparable to that-shown on the graph for nickel carbonyl.

The apparatus and method of the invention makes possible the deposition of metal by gas plating substantially uniformly throughout the porous body. This is accomplished by modifying the gas plating procedure and observing the critical conditions as hereinbefore described.

It will also be understood that while there have been described and illustrated certain specific embodiments of the invention, it is not intended to thereby limit the same thereto since the invention is readily susceptible to various modifications, and the use of diiferent thermally decomposable metal bearing compounds, and substitutions of different porous substrate materials, and such as may occur to those skilled in the art, all of which come within the scope of this invention, and as set forth in .the appended claim.

What is claimed is:

body and wherein the porous body is metallized substantally uniformly throughout the body thereof, said method 7 comprising positioning said abrasive body in an enclosure,

radiantly heating the porous body to be treated While enclosed by directing infra-red heat rays onto one side only of said porous body, forcing gaseous plating within the body from 250 F. to 500 F., passing gaseous plating mixture comprising a heat-decomposable metal compound through said porous body from the other side thereof to the said one side while heated at said temperature gradient, said gaseous mixture including a minor percent amount of a carrier gas and Where thermal decomposition of the metal compound takes place to plate metal on the porous body walls evenly throughout said body.

References Cited by the Examiner UNITED STATES PATENTS 2,224,400 12/40 Sendzimer 118-641 2,602,033 7/52 Lander 117-1072 2,638,423 5/53 Davis et al. 117-1072 X 2,653,879 9/53 Fink 117-1072 2,770,212 11/56 Marantz 118-641 2,789,038 4/57 Bennett et al. 117-46 X 2,813,803 11/57 Homer et al. 117-1072 2,833,676 5/58 I-Ieibel et al. 117-107.2 X 2,847,319 8/58 Marvin 117-1072 X 2,883,708 4/59 Sem 264-81 X 2,896,570 7/59 Nacket' a1 117-1072 X 2,916,400 12/59 Homer 117-1072 3,031,340 4/62 Girardot 117-1072 X 3,037,999 6/62 Ihrman et al. 117-1072 3,075,494 1/63 Toulmin 117-1072 X RICHARD D. NEVIUS, Primary Examiner. 

